Cannot set focus to the TextField inside ExpansionTile programmaticaly - flutter

Question

I have an ExpansionTile with a TextField inside and trying to set the focus to this text field when user expands the tile. But for some reasons I can't get it working.
Here is the code:
ExpansionTile(
key: PageStorageKey<String>("notes_key"),
title: Text(
"Notes",
style: TextStyle(color: Colors.indigo),
),
onExpansionChanged: (expanded){
if(expanded){
FocusScope.of(context).requestFocus(_notesFocusNode);
_notesController.value = _notesController.value.copyWith(text: _notes);
} else {
_notesFocusNode.unfocus();
}
},
children: <Widget>[
Row(
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Expanded(
child: TextField(
decoration: InputDecoration(
border: InputBorder.none,
),
textInputAction: TextInputAction.newline,
style: TextStyle(color: Colors.black),
keyboardType: TextInputType.multiline,
focusNode: _notesFocusNode,
controller: _notesController,
key: PageStorageKey("notes_field_key"),
minLines: 1,
maxLines: null,
onChanged: (value) => _notes = value,
),
),
IconButton(
icon: Icon(Icons.done),
color: Colors.teal,
onPressed: () => _notesFocusNode.unfocus(),
),
],
),
],
)
Any help appreciated.
For a bigger context, the text field is not inside any form. The provided piece of code lays inside the bigger one, where it is wrapped in the ListView. Probably I need to have some parent focus scope in my view?

Answer 1

The TextFormField is not yet available to get Focus when you expand the Tile. It only becomes available after a few milliseconds of the animation starting. Since you don't have a way to know when the animation has finished, you can make a workaround by adding a delay. I would advise a minimum of 200 milliseconds so that the animation doesn't stagger but the TextFormField gets focus:
Future.delayed(Duration(milliseconds: 200), (){
FocusScope.of(context).requestFocus(_notesFocusNode);
});